With the end of cheap oil and the mounting peak of world oil production, it is recognized that petroleum is a non-renewable resource and will eventually be depleted. This realization has sparked a renewed interest in the development of renewable sources for fuel. This is particularly true in the case of aviation fuels used in internal combustion engines, such as in turbine engines as well as for jet fuels.
In the United States, the Federal Aviation Administration (FAA) is responsible for setting the technical standards for aviation fuels through the American Society for Testing and Materials (ASTM). Currently, the FAA uses as a standard for aviation fuel the 100LL aviation gasoline. To qualify as a 100 octane aviation fuel, any new fuel must comply with the current aviation gasoline specification ASTM D910. This is true whether the new fuel is based on petroleum or a chemical or chemical combination.
Ethanol-based fuels for internal combustion engines have been available for roughly five decades. The State of California originated mandatory oxygenation of motor fuels, which includes ethanol-based fuels, partly to decrease the wholesale cost of fuel, and to a lesser extent to reduce air pollution per gallon of gasoline consumed. Effectively, since ethanol-based fuels have lower energy, pollution is generally increased per mile. A key benefit of ethanol-based fuels is that they have a slightly higher octane number than ethanol-free gasoline. This is the reason many oil companies provide high ethanol containing premium fuels and lower ethanol regular grades of gasoline. Renewable fuels made from some chemical species other than ethanol have been found to exhibit significantly higher octane numbers and increased energy per unit volume when compared to commercial fuels and ethanol-based fuels.
Octane (Power)
Octane number is a measure of the effectiveness of power production. It is a kinetic parameter, therefore difficult to predict. Oil companies compiled volumes of experimental octane data (for most hydrocarbons) for the Department of Defense in the 1950's. The method used to obtain this dynamic parameter is discussed in the next paragraph. 2,2,4-trimethyl pentane (isooctane) has a defined octane number of 100, and n-heptane has a defined octane number of 0, based on experimental tests. Octane numbers are linearly interpolated and extrapolated by this method; hence predictions for mixes can be made once pure sample values are determined.
Automobile gasoline is placarded at the pump as the average of Research and Motor octane numbers. These correlate to running a laboratory test engine (CFR) under less severe and more severe conditions, respectively. True octane numbers lie between the Research and Motor octane values. Aviation fuel has a “hard” requirement of 100 MON (motor octane number); ethanol has a MON of 96, which makes its use only viable when mixed with other higher octane components. Conventional 1OOLL (i.e., 100 octane low lead) contains about 3 ml of tetraethyl lead per gallon.
Range (Energy)
The inherent energy contained within gasoline is directly related to mileage, not to octane number. Automobile gasoline has no energy specification, hence no mileage specification. In contrast, aviation fuels, a common example being 100LL (100 octane low lead), have an energy content specification. This translates to aircraft range and to specific fuel consumption. In the octane examples above, i-octane and n-heptane had values of 100 and 0, respectively. From an energy perspective, they contain heat of combustion values of 7.84 and 7.86 kcal/ml, respectively, which is the reverse of what one would expect based on power developed. Aircraft cannot compromise range due to the sensitivity of their missions. For this reason, energy content is equally important as MON values.
The current production volume of 100LL is approximately 850,000 gallons per day. 100LL has been designated by the Environmental Protection Agency (EPA) as the last fuel in the United States to contain tetraethyl lead. This exemption will likely come to an end in the near future (2010).
Although a number of chemical compounds have been found to satisfy the motor octane number for 100LL octane aviation fuel, they fail to meet a number of other technical requirements for aviation fuel. This is true, for example, for isopentane, 90MON, and trimethyl benzene 136MON. For example, pure isopentane fails to qualify as an aviation fuel because it does not pass the ASTM specification D909 for supercharge ON, ASTM specification D2700 for motor octane number, and ASTM specification D5191 for vapor pressure. Pure sym-trimethyl benzene (mesitylene) also fails to qualify as an aviation fuel because it does not pass ASTM specification D2386 for freeze point, ASTM specification D5191 for vapor pressure, and ASTM specification D86 for the 10% distillation point.
The fermentation of a biomass using microbes to produce acetone and butanol was first discovered by Chaim Weizmann in 1916 and is described in U.S. Pat. No. 1,315,585 and other corresponding patents throughout the world. This process known as the Weizmann process was used by both Great Britain and the United States in World Wars I and II to produce acetone for the production of cordite used in making smokeless powder. Unfortunately, this method is energy intensive, and accordingly uneconomical.
A number of methods are known for making mesitylene from acetone and include, for example:                (1) Liquid phase condensation in the presence of strong acids, e.g. sulfuric acid and phosphoric acid as described in U.S. Pat. No. 3,267,165 (1966);        (2) Vapor phase condensation with tantalum containing catalysts as described in U.S. Pat. No. 2,917,561 (1959);        (3) Vapor phase condensation using as catalyst the phosphates of the metals of group IV of the periodic system of elements, e.g. titanium, zirconium, hafnium and tin as described in U.S. Pat. No. 3,94,079 (1976);        (4) Vapor phase reaction in the presence of molecular hydrogen and a catalyst selected from alumina containing chromia and boria as described in U.S. Pat. No. 3,201,485 (1965);        (5) Vapor phase reaction using catalysts containing molybdenum as described in U.S. Pat. No. 3,301,912 (1967) or tungsten as described in U.S. Pat. No. 2,425,096, a vapor phase reaction over a niobium supported catalyst with high selectivity. The catalyst is preferably made by impregnating a silica support with an ethanolic solution of NCl5 or an aqueous solution of Nb in order to deposit 2% Nb by weight and by calcining the final solid at 550° C. for 18 hours. At 300° C., the condensation of acetone produces mainly mesitylene (70% selectivity) at high conversion (60-80% wt) as described in U.S. Pat. No. 5,087,781.        
It is also known in the art to dimerize acetone to form isopentane. This process involves first dimerizing acetone to form diacetone alcohol which is then dehydrated to form mesitytl oxide. The mesityl oxide then undergoes gas phase reformation hydrogenation to form isopentane.
It is also known from U.S. Pat. No. 7,141,083 to produce a fuel comprising mesitylene and straight-chain alkanes (i.e., hexanes, heptanes, octanes, nonanes and the like) from plant oil, such as corn oil. The composition of corn oil is shown in Table 1 below. The predominant components of corn oil are stearic, palmitic, oleic, and linoleic acids of the free fatty acids.
It is an object of the present invention to provide biogenic fuels that effectively replace petroleum-based fuels currently used in engines.
It is another object of the present invention to provide fully renewable fuels for other internal combustion/heat engines as well.
It is a further object of the present invention to provide high energy renewable fuels for use in turbines and other heat engines by the same methodology; the energy content and physical properties of the renewable components being tailored to the type of engine to be fueled.
It is another object of the present invention to provide a binary mixture of components which meet the technical specifications for turbine engines.
It is another object of the present invention to provide a non-petroleum based aviation fuel which meets the technical specifications of the Federal Aviation Administration for petroleum-based turbine fuels.
It is still another object of the present invention to provide a process for the production from a biomass of the components of binary chemicals and ternary mixtures which satisfy the technical specifications for both turbine and diesel engines.